1. Field of the Invention
The present invention relates to a tension adjuster and, more specifically to an improved tensioner for the adjustment of tension in a chain or belt of a power transmission mechanism.
2. Description of the Prior Art
Chain and belt driven power transmission mechanisms are utilized in a variety of applications, including, but not limited to, machinery, bicycles, motorcycles, chain saws, lawnmowers and the like. In general, a drive sprocket or pulley is attached to a drive shaft. The drive shaft and drive sprocket or pulley being driven either manually by a user or automatically by a motor of some type. The drive sprocket or pulley is then coupled to a flexible power transmission mechanism such as a chain or belt. The chain or belt is then coupled to a second sprocket or pulley which is attached to a driven shaft. As the drive sprocket or pulley is rotated, either manually or by a motor, the chain or belt turn in relation to the drive sprocket or pulley thereby rotating the driven sprocket or pulley and the connected driven shaft.
Every application of a chain or belt driven power transmission system has its own unique specifications and requirements for chain or belt driven power transmission. One of the more common requirements is that the chain or belt must have the correct tension to efficiently transfer power from the drive sprocket or pulley to the driven sprocket or pulley.
For example, in everyday bicycling, a past time many people enjoy, the means for maintaining the proper tension on the rear axle and driven sprocket of the bicycle are typically simple lock washers and nuts that hold the axle in place on the rear yoke once the proper tension on the chain and sprocket arrangement has been achieved. However, in the sport of BMX bicycling or “extreme bicycling” the participants have specialized bicycles designed to fit their specific needs. In particular, many of the bicycles have what is commonly called “pegs” mounted onto both sides of both of the front and rear wheel axles. FIG. 1 depicts the prior art pegs 12 as they are mounted onto the rear axle of a bicycle. The pegs 12 extend outward from the wheel axle about 4 or 5 inches. There are many uses for these pegs in extreme bicycling however, one of the more common uses is to ride the bicycle up and off of a curved surface or ramp and then use one side of the rear pegs 12 to “ride” the bicycle along a railing.
While this stunt and other similar ones are both tricky and impressive, there are some drawbacks to the bicycle in doing these stunts, as will be explained below. As is well known in the construction of bicycles, there is generally a split open-ended “yoke” 8 into which the axles of the wheel and tire sits. On the rear axle there is a chain driven sprocket attached to the rear wheel axle. This driven sprocket is rotatably attached to the bicycle chain for providing momentum to the bicycle and rider through a chain drive sprocket and pedal arrangement located beneath the rider. Of necessity, the rear wheel and driven sprocket, the chain and the drive sprocket and pedal arrangement need to be kept in a relatively tight arrangement in order to keep a proper amount of tension on the chain to provide maximum power transfer and to prevent the chain from disengaging from either sprocket which could otherwise cause accidents and/or injury.
In the performance of the BMX moves as described above, the weight and force of the rider and bicycle landing on a peg 12 and riding along a rail for a short distance can cause the rear axle and driven sprocket arrangement to be forced inward on the yoke 8, thereby causing tension in the chain 9 to be reduced and/or lost entirely. To solve this problem of loosening chains, there are a number of chain tensioners currently available on the market.
FIGS. 2 and 3 depict a conventional prior art bicycle chain tension adjuster 1 which is a longitudinal plate 2 having a hole 3 defined laterally therethrough and a threaded rod 4 fixedly attached to the plate 2. A slidable retaining bar 5 fits over the threaded rod 4 and a lock nut 6 is threaded onto the threaded rod 4. As shown in FIG. 3, the hole 2 in the chain tensioner 1 is placed over the axle 7. The axle 7 is placed in the bicycle yoke 8 in this example. The retaining bar 5 fits over the open end of the yoke 8. As the lock nut 6 is turned in, the lock nut 6 pushes the retaining bar 5 into contact with the ends of the yoke 8 thereby pulling the plate 2 and axle 7 backwards to tighten the chain 9. Once the proper tension has been achieved, the position of the tensioner 1 and axle 7 are held in place by a washer 10 and nut 11.
Unfortunately, all of the tensioners found by the inventor suffer from the same problem. The problem being that the current chain tensioners 1 have a threaded rod 4 or other protrusion extending out past the rear of the yoke 8. When performing the extreme bicycling maneuver described above, (i.e.; riding the bicycle on a peg 12 on a rail), when executing and landing this maneuver, it often happens that the threaded tensioning rod 4 and retaining bar 5 strike the rail instead of just the peg 12 because the retaining bar 5 and rod 4 or other protrusion stick out past the end of the yoke 8. This can result in loosening the chain tension thereby causing the bicycle to operate improperly or not at all. In addition, the above stated maneuver sometimes damages and/or destroys the tensioner by breaking the threaded rod off thereby losing tension to the chain and sprocket arrangement. This can prevent the cyclist from riding the rail successfully, resulting in injury to the rider and further damage to the bicycle if the bicycle and rider fall off the rail to the hard ground from a reasonably high height and speed in the air.
Other applications where a low profile chain or belt tensioner would be advantageous could be in motorcycles, lawnmowers, machinery, chain saws and the like.
The present invention provides a low profile chain and belt tensioner to mitigate or obviate the aforementioned problems.